Inside Our Earth
The earth is made up of several concentric layers with one inside another. The structure of the earth’s interior is fundamentally divided into three layers – crust, mantle, and core. The crust forms only 1 percent of the volume of the earth, 84 percent consists of the mantle and 15 percent makes the core.The radius of the earth is 6371 km.
Crust
- The uppermost layer over the earth’s surface is called the crust.
- It is the thinnest of all the layers. It is about 35 km. on the continental masses and only 5 km. on the ocean floors.
- The main mineral constituents of the continental mass are silica and alumina. It is thus called sial (si-silica and al-alumina).
- The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium).
- The discontinuity between the hydrosphere and crust is termed as the Conrad Discontinuity.
Manlte
- Just beneath the crust is the mantle which extends up to a depth of 2900 km below the crust.
- The discontinuity between the crust and mantle is called as the Mohorovich Discontinuity or Moho discontinuity.
- The uppermost solid part of the mantle and the entire crust constitute the Lithosphere.
- The asthenosphere (in between 80-200km) is a highly viscous, mechanically weak and ductile, deforming region of the upper mantle which lies just below the lithosphere.
- The asthenosphere is the main source of magma and it is the layer over which the lithospheric plates/ continental plates move (plate tectonics).
- The discontinuity between the upper mantle and the lower mantle is known as Repetti Discontinuity.
- The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere.
Core
- The innermost layer is the core with a radius of about 3500 km.
- It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous i.e. iron).
- The central core has very high temperature and pressure.
- The core is separated from the mantle by Guttenberg’s Discontinuity.
- The core is the densest layer of the earth.
- The discontinuity between the upper core and the lower core is called as Lehmann Discontinuity.
- Barysphere is sometimes used to refer the core of the earth or sometimes the whole interior.
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